1. Technical Field
The present disclosure relates to a radio communication apparatus with a function of detecting interference caused by an adjacent-channel signal and to an interference detection method.
2. Description of the Related Art
In recent years, standards for short-distance radio systems that use the 60 GHz band, such as the IEEE802.11ad standard, have been set and each country allocates frequencies to a maximum of four channels.
FIG. 11 illustrates the allocation of radio channels used in IEEE802.1 lad. As illustrated in FIG. 11, four radio channels (ch) are used at the maximum in Japan. The respective specified center frequencies of the channels are 58.32 GHz, 60.48 GHz, 62.64 GHz, and 64.80 GHz while the center frequencies of adjacent ones of the channels are 2.16 GHz apart.
The sampling rate of a single-carrier modulated wave or a transmission signal based on the IEEE802.11ad standard is 1.76 GHz, and under ideal circumstances, no interference occurs among adjacent channels and communication is possible using a plurality of channels at the same time. In an actual transmitter, however, a factor typified by characteristic distortion of a high-frequency circuit, such as an amplifier, causes power leakage to an adjacent channel. The permissible amount of such power leakage is specified as a transmission mask in the IEEE802.11ad standard.
The amount of power leakage from an adjacent channel is generally small. However, when another radio communication apparatus using the adjacent channel comes closer to a radio communication apparatus at a local station, the amount of the power leakage received at the local station from the adjacent channel becomes no more negligible and the quality of communication at the local station is lowered. This is called adjacent-channel interference.
When a radio communication apparatus is affected by adjacent-channel interference, the adjacent-channel interference is controlled so as to be avoided or suppressed. For example, the radio channel that the local station has used is changed to another channel, or another radio communication apparatus, which is an interfering station causing the interference, is requested to reduce transmission power. In another example, when adjacent-channel interference is detected, the characteristics of a reception filter of a receiver at the local station are changed.
To avoid or suppress such interference effectively, it is necessary to detect that adjacent-channel interference is occurring, with high reliability. That is, it is necessary to distinguish the interference from another kind of interference, such as co-channel interference. It is also necessary to identify the radio channel that the interfering station uses.
A technique for detecting interference caused by an adjacent-channel signal uses measurement of a spectrum of an undesired signal as discussed in, for example, U.S. Pat. No. 7,039,093. Another technique, which is for determining whether the adjacent-channel interference is from a high-frequency channel or a low-frequency channel, uses a high-pass filter to extract interference wave components as discussed in, for example, Japanese Unexamined Patent Application Publication (Translation of PCT Application) No. 2010-521893.